It is common knowledge that in cut-and-fill stoping operations, the fill phase frequently presents serious difficulties which prevent continuous, stable and highly mechanized mine production.
Over the last decades, mechanic fill has been replaced in various mines by fluid fills, such as hydraulic and pneumatic fills. In these methods, the fill is prepared in adequate places, and then is distributed through pipes, allowing a larger production at lower cost.
The use of a large portion of the slurry or tailings of a concentrating plant as a component of the fluid fill in an underground operation satisfies the following main objectives:
Structural support of the mined out zones; and
Underground storage of the tailings from the concentrating plants.
As a structural support, the fluid fill, once solidified, is one of various possible systems in mining.
As an underground system of disposing of the tailings of a concentrator, the hydraulic fill is many a time an imperative procedure for ecological reasons, or because of lack of an adequate place to store it on the surface.
Even though fluid fills represent a step forward in the technique of preparing and distributing the fill internally within the mine (as compared with mechanical fill), complex problems still subsist.
In the case of orebodies in heavy ground, the descending method of cut-and-fill uses intermediate concrete slabs such as is shown in FIG. 1. The tailing-cement ratio in slabs 1, 2 and 3 can be 6 to 1, and in the rest of the fill, identified as 4 and 5, the ratio can be 20 to 1.
In the case of vertical or steep veins, the ascending method of cut-and-fill is employed, often using cement slabs at the top of each fill phase. In such an application, the tailings to cement ratio may be 10 to 1 in the slab, and very much larger in the remaining portion of the fill.
Some of the disadvantages and problems of fluid fills are as follows:
Only the coarse component of the tailings are adequate to provide structural function in hydraulic fill, thus there remains an ecological and storage problem with the fine component of the tailing, or slimes which can amount in certain cases up to 50% of the tailings at the concentrator.
The fill material in the stopes blocks access haulage and ventilation throughout the mined areas once these are filled, necessitating often the driving of haulage and ventilation galleries off the ore, which is costly and utilizes mine equipment for non-productive purposes.
In other cases, in which principal galleries must be kept open through a backfill area, there is need to construct artifical timbered tubes, as in FIG. 6, or costly steel tubes in the stopes as in FIG. 7, prior to the application of the fill.
The weight of the fill material sometimes presents serious structural problems in structural stability, particularly in the descending cut and fill method shown in FIG. 1.
The transportation of the tailings from plant to mine is often costly, and sometimes not feasable if there is a great difference of elevation between mine and plant.
Such problems in fill back operations as reviewed above are solved, and new beneficial features of hydraulic and pneumatic fill are made possible, by means of the apparatus and methods of the present invention, in which inflatable, or fluid filled structures are immersed in fillback material with cement, as is described hereafter in the invention, to define hollow permanent tubular accessways and haulageways within the solidified fill. Sufficient advantages stem from the method to permit using low cost cemented or concrete fill in mining.
Such earlier work which has been done with inflatable systems in mining do not cover the subject of the present invention as can be seen by comparing the specifications and drawings of the present invention to those of the following prior art:
U.S. patent application Ser. No. 356,591 now U.S. Pat. No. 3,937,025 of Alvarez Calderon, related to the use of inflatable bags to keep fill away from the side of a stope:
French Pat. No. 1.008.534 of Haarmann teaches the use of tubular structures in mines to support the roof of the stope;
German Pat. 1.069.549 teaches the use of multicellular inflatable tubes supported by roof and floor for lateral containment of backfill.